There’s no simple answer to this one, as it depends on the climate you live in. Is your winter harsh and long? Then you will probably need to foresee some extra measures to keep your plants from freezing. Is your climate more moderate and does it only freeze during a short amount of time and not very hard? Then you can probably get along by insulating your greenhouse and making sure it gets plenty of sunshine to heat up during the day.
The best way to make sure your plants are not freezing, is by installing a thermometer in the greenhouse and keeping a close eye on it. When the temperature drops below freezing point, you can insulate your greenhouse or add greenhouse heaters.Prepare your greenhouse for winter